"Over most conventional measurement periods, an increase in wealth simply reflects the willingness of other investors to pay a higher price for the assets that you bought somewhat earlier. Seen in those terms, what we like to consider as our wealth has a far more evanescent and transitory character than most of us are ready to admit. What appears to be ours, in other words, is ours only by leave of the rest of the fraternity of investors, not one of whom is in any way committed to paying up for what we hold. They own the option, not each of us as individuals."